Commercial printing apparatuses such as computer printers, plotters, copiers, and facsimile machines employ inkjet technology for producing images and text on print media. A conventional inkjet printer implements one or more inkjet cartridges, called “pens” by those in the art, to eject droplets of ink onto a print medium, e.g. paper. Each pen has a printhead formed with a plurality of small nozzles through which the ink droplets are ejected. The pens are typically mounted on a movable carriage. To print an image or text, the carriage traverses back and forth across the print medium in a direction traverse to the moving direction of the print medium. Each passage or scan of the carriage across the print medium prints a “swath.” For each swath, the nozzles are fired to print groups of dots. After each swath is printed, the print medium is advanced relative to the carriage so that a subsequent swath may be printed. By repetition of this process, a completed printed page may be produced.
When the carriage is scanned across the paper, the carriage velocity is not constant. There are acceleration and deceleration ramps at the ends of a scan. In recent trend to downsize the printing apparatus, the so-called “printing on the ramp” has been introduced. In printing on the ramp, printing is performed during the acceleration and deceleration ramps. One advantage of this printing method is that the time required to print a swath is reduced, thereby improving throughput. In addition, the required traversing distance of the carriage is reduced, thereby enabling size reduction for the printing apparatus. However, printing during acceleration and deceleration ramps introduces ink dot placement errors (DPE) in the scanning direction of the carriage. These errors have to be compensated in order to improve print quality. Because each inkjet printing apparatus is made up of many different parts and each part is subjected to its own manufacturing imperfection, the amount of compensation would vary among different apparatuses. Thus, there exists a need for a method of printing during acceleration and deceleration of the carriage with compensation for errors in ink dot placement.